1. Field of the Invention
The present invention relates to an optical information recording/reproducing apparatus, for example, a reader-writer an for optical card, in which a plurality of beams are guided simultaneously to irradiate a reciprocating information recording medium and to form light spots thereon, so as to enable recording and verification (immediate reproduction of recorded information) both forward and backward in the reciprocating motion of the recording medium.
2. Related Background Art
A typical example of such an optical information recording/reproducing apparatus is an optical card information recording/reproducing apparatus having the structure as shown in FIG. 1, which is conventionally used. In the apparatus, recording and reproduction of information are carried out with beams from separate light sources (which is generally called a double light source method) to avoid degradation of reproducing light and to achieve high speed recording with verification.
An information recording medium used herein (as denoted by reference numeral 1 in FIG. 1) is in the form of a disk or card which is composed of a substrate such as glass and plastic, and a record layer formed thereon. Semiconductor lasers 21, 22 are used as the two light sources in the information recording/reproducing apparatus in order to record information in the information recording medium 1 and to reproduce the information therefrom or in order to reproduce the information at the same time as the recording to verify the recorded information. One laser emits light with a wavelength of 780 nm and the other omits light with a wavelength of 830 nm. Each emitted light is collimated by a collimator lens 23 or 24. The former light passes through a diffraction grating 25 to be split into zeroth-order diffracted light and .+-.first-order diffracted light, while the latter light directly enters a dichroic prism 26. The prism 26 is so designed that dielectric multilayers layered on a prism bond surface as shown in FIG. 2 transmit the light with a wavelength of 780 nm in the form of a p-polarization component and reflects the light with a wavelength of 830 nm in the form of p-polarization component. Each beam outgoing from the prism 26 passes through a beam shaping prism 27 to be shaped to have a predetermined light distribution. Then the shaped beam enters a polarization beam splitter 28 having the property as shown in FIG. 3 then to enter a quarter-wave plate 29 to be circularly polarized. The circularly polarized beam reaches an objective lens 30. Each beam is converged by the objective lens 30 on the information recording medium 1, so that the light with a wavelength of 780 nm forms three light spots S.sub.1 (+first-order diffracted light), S.sub.2 (zeroth-order diffracted light) and S.sub.3 (-first-order diffracted light), and that the light with wavelength of 830 nm forms a light spot S.sub.w.
The light spots are positioned on an information track 2 on the information recording medium 1 in an example of an information recording medium of a card as shown in FIG. 4 and FIG. 5. Specifically, information tracks 2 are arranged from a home position 3 in the order of 2-1, 2-2, 2-3, . . . and tracking tracks 4-1, 4-2, 4-3, . . . are juxtaposed adjacent to the information tracks. Address portions 6-1, 6-2, . . . and 7-1, 7-2, . . . are prepared for track identification on either side of the information tracks. The light spots S.sub.1, S.sub.3 are positioned on two tracking tracks 4 adjacent to each other, and the light spot S.sub.2 on an information track 2 between the two adjacent tracking tracks. Numeral 51 denotes a drive motor for moving the information recording medium 1 forward and backward (in the direction F and in the direction L), which effects a relative reciprocating motion of the information recording medium 1 to an optical head 50 in parallel with the information tracks 2.
Reflected light from the information recording medium passes through the same optical path up to the polarization beam splitter 28 and is then deflected thereby. The deflected light passes through a band pass filter 31 having the property equivalent to that shown in FIG. 2 and then reaches a toric lens 33 having a special film with the property shown in FIG. 6. The toric lens 33 transmits only light with a wavelength of 780 nm, and the transmitted light reaches a photodetector 34. Numeral 32 designates a stopper for receiving light reflected by the band pass filter 31. The photodetector 34 has receptor elements 11, 13 for obtaining tracking control signals and a receptor element 12 sectioned into four segments for detecting focus control signals and reproduction signals, as shown in FIG. 7.
In the conventional example as described, however, the verification is possible only in one direction (in the direction F in FIG. 5) on the reciprocating (moving in the direction F and in the direction L) information recording medium. The verification is impossible in the return direction (in the direction L in FIG. 5), since the reproducing light spot S.sub.2 is leading the recording light spot S.sub.w.
Also, Japanese Laid-open Patent Application No. 61-240408 discloses an optical information recording/reproducing apparatus which can perform recording and reproduction of information in a relative reciprocating motion between a recording/reproducing apparatus and a recording medium, in which information recorded in the forward motion is read out in the backward direction during return, and the thus read information is compared with information desired to be recorded thereby to check whether information is correctly recorded on the medium.
This method, however, cannot enable the recording and verification of information in both directions in a reciprocating motion of an information recording medium.